[mirror_ubuntu-bionic-kernel.git] / arch / parisc / math-emu / sfadd.c

/*
 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
 *
 * Floating-point emulation code
 *  Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
 *
 *    This program is free software; you can redistribute it and/or modify
 *    it under the terms of the GNU General Public License as published by
 *    the Free Software Foundation; either version 2, or (at your option)
 *    any later version.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU General Public License for more details.
 *
 *    You should have received a copy of the GNU General Public License
 *    along with this program; if not, write to the Free Software
 *    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
/*
 * BEGIN_DESC
 *
 *  File:
 *	@(#)	pa/spmath/sfadd.c		$Revision: 1.1 $
 *
 *  Purpose:
 *	Single_add: add two single precision values.
 *
 *  External Interfaces:
 *	sgl_fadd(leftptr, rightptr, dstptr, status)
 *
 *  Internal Interfaces:
 *
 *  Theory:
 *	<<please update with a overview of the operation of this file>>
 *
 * END_DESC
*/


#include "float.h"
#include "sgl_float.h"

/*
 * Single_add: add two single precision values.
 */
int
sgl_fadd(
    sgl_floating_point *leftptr,
    sgl_floating_point *rightptr,
    sgl_floating_point *dstptr,
    unsigned int *status)
    {
    register unsigned int left, right, result, extent;
    register unsigned int signless_upper_left, signless_upper_right, save;
    
    
    register int result_exponent, right_exponent, diff_exponent;
    register int sign_save, jumpsize;
    register boolean inexact = FALSE;
    register boolean underflowtrap;
        
    /* Create local copies of the numbers */
    left = *leftptr;
    right = *rightptr;

    /* A zero "save" helps discover equal operands (for later),  *
     * and is used in swapping operands (if needed).             */
    Sgl_xortointp1(left,right,/*to*/save);

    /*
     * check first operand for NaN's or infinity
     */
    if ((result_exponent = Sgl_exponent(left)) == SGL_INFINITY_EXPONENT)
	{
	if (Sgl_iszero_mantissa(left)) 
	    {
	    if (Sgl_isnotnan(right)) 
		{
		if (Sgl_isinfinity(right) && save!=0) 
		    {
		    /* 
		     * invalid since operands are opposite signed infinity's
		     */
		    if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
                    Set_invalidflag();
                    Sgl_makequietnan(result);
		    *dstptr = result;
		    return(NOEXCEPTION);
		    }
		/*
	 	 * return infinity
	 	 */
		*dstptr = left;
		return(NOEXCEPTION);
		}
	    }
	else 
	    {
            /*
             * is NaN; signaling or quiet?
             */
            if (Sgl_isone_signaling(left)) 
		{
               	/* trap if INVALIDTRAP enabled */
		if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
        	/* make NaN quiet */
        	Set_invalidflag();
        	Sgl_set_quiet(left);
        	}
	    /* 
	     * is second operand a signaling NaN? 
	     */
	    else if (Sgl_is_signalingnan(right)) 
		{
        	/* trap if INVALIDTRAP enabled */
               	if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
		/* make NaN quiet */
		Set_invalidflag();
		Sgl_set_quiet(right);
		*dstptr = right;
		return(NOEXCEPTION);
		}
	    /*
 	     * return quiet NaN
 	     */
 	    *dstptr = left;
 	    return(NOEXCEPTION);
	    }
	} /* End left NaN or Infinity processing */
    /*
     * check second operand for NaN's or infinity
     */
    if (Sgl_isinfinity_exponent(right)) 
	{
	if (Sgl_iszero_mantissa(right)) 
	    {
	    /* return infinity */
	    *dstptr = right;
	    return(NOEXCEPTION);
	    }
        /*
         * is NaN; signaling or quiet?
         */
        if (Sgl_isone_signaling(right)) 
	    {
            /* trap if INVALIDTRAP enabled */
	    if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
	    /* make NaN quiet */
	    Set_invalidflag();
	    Sgl_set_quiet(right);
	    }
	/*
	 * return quiet NaN
 	 */
	*dstptr = right;
	return(NOEXCEPTION);
    	} /* End right NaN or Infinity processing */

    /* Invariant: Must be dealing with finite numbers */

    /* Compare operands by removing the sign */
    Sgl_copytoint_exponentmantissa(left,signless_upper_left);
    Sgl_copytoint_exponentmantissa(right,signless_upper_right);

    /* sign difference selects add or sub operation. */
    if(Sgl_ismagnitudeless(signless_upper_left,signless_upper_right))
	{
	/* Set the left operand to the larger one by XOR swap *
	 *  First finish the first word using "save"          */
	Sgl_xorfromintp1(save,right,/*to*/right);
	Sgl_xorfromintp1(save,left,/*to*/left);
	result_exponent = Sgl_exponent(left);
	}
    /* Invariant:  left is not smaller than right. */ 

    if((right_exponent = Sgl_exponent(right)) == 0)
        {
	/* Denormalized operands.  First look for zeroes */
	if(Sgl_iszero_mantissa(right)) 
	    {
	    /* right is zero */
	    if(Sgl_iszero_exponentmantissa(left))
		{
		/* Both operands are zeros */
		if(Is_rounding_mode(ROUNDMINUS))
		    {
		    Sgl_or_signs(left,/*with*/right);
		    }
		else
		    {
		    Sgl_and_signs(left,/*with*/right);
		    }
		}
	    else 
		{
		/* Left is not a zero and must be the result.  Trapped
		 * underflows are signaled if left is denormalized.  Result
		 * is always exact. */
		if( (result_exponent == 0) && Is_underflowtrap_enabled() )
		    {
		    /* need to normalize results mantissa */
	    	    sign_save = Sgl_signextendedsign(left);
		    Sgl_leftshiftby1(left);
		    Sgl_normalize(left,result_exponent);
		    Sgl_set_sign(left,/*using*/sign_save);
		    Sgl_setwrapped_exponent(left,result_exponent,unfl);
		    *dstptr = left;
		    return(UNDERFLOWEXCEPTION);
		    }
		}
	    *dstptr = left;
	    return(NOEXCEPTION);
	    }

	/* Neither are zeroes */
	Sgl_clear_sign(right);	/* Exponent is already cleared */
	if(result_exponent == 0 )
	    {
	    /* Both operands are denormalized.  The result must be exact
	     * and is simply calculated.  A sum could become normalized and a
	     * difference could cancel to a true zero. */
	    if( (/*signed*/int) save < 0 )
		{
		Sgl_subtract(left,/*minus*/right,/*into*/result);
		if(Sgl_iszero_mantissa(result))
		    {
		    if(Is_rounding_mode(ROUNDMINUS))
			{
			Sgl_setone_sign(result);
			}
		    else
			{
			Sgl_setzero_sign(result);
			}
		    *dstptr = result;
		    return(NOEXCEPTION);
		    }
		}
	    else
		{
		Sgl_addition(left,right,/*into*/result);
		if(Sgl_isone_hidden(result))
		    {
		    *dstptr = result;
		    return(NOEXCEPTION);
		    }
		}
	    if(Is_underflowtrap_enabled())
		{
		/* need to normalize result */
	    	sign_save = Sgl_signextendedsign(result);
		Sgl_leftshiftby1(result);
		Sgl_normalize(result,result_exponent);
		Sgl_set_sign(result,/*using*/sign_save);
                Sgl_setwrapped_exponent(result,result_exponent,unfl);
		*dstptr = result;
		return(UNDERFLOWEXCEPTION);
		}
	    *dstptr = result;
	    return(NOEXCEPTION);
	    }
	right_exponent = 1;	/* Set exponent to reflect different bias
				 * with denomalized numbers. */
	}
    else
	{
	Sgl_clear_signexponent_set_hidden(right);
	}
    Sgl_clear_exponent_set_hidden(left);
    diff_exponent = result_exponent - right_exponent;

    /* 
     * Special case alignment of operands that would force alignment 
     * beyond the extent of the extension.  A further optimization
     * could special case this but only reduces the path length for this
     * infrequent case.
     */
    if(diff_exponent > SGL_THRESHOLD)
	{
	diff_exponent = SGL_THRESHOLD;
	}
    
    /* Align right operand by shifting to right */
    Sgl_right_align(/*operand*/right,/*shifted by*/diff_exponent,
     /*and lower to*/extent);

    /* Treat sum and difference of the operands separately. */
    if( (/*signed*/int) save < 0 )
	{
	/*
	 * Difference of the two operands.  Their can be no overflow.  A
	 * borrow can occur out of the hidden bit and force a post
	 * normalization phase.
	 */
	Sgl_subtract_withextension(left,/*minus*/right,/*with*/extent,/*into*/result);
	if(Sgl_iszero_hidden(result))
	    {
	    /* Handle normalization */
	    /* A straightforward algorithm would now shift the result
	     * and extension left until the hidden bit becomes one.  Not
	     * all of the extension bits need participate in the shift.
	     * Only the two most significant bits (round and guard) are
	     * needed.  If only a single shift is needed then the guard
	     * bit becomes a significant low order bit and the extension
	     * must participate in the rounding.  If more than a single 
	     * shift is needed, then all bits to the right of the guard 
	     * bit are zeros, and the guard bit may or may not be zero. */
	    sign_save = Sgl_signextendedsign(result);
            Sgl_leftshiftby1_withextent(result,extent,result);

            /* Need to check for a zero result.  The sign and exponent
	     * fields have already been zeroed.  The more efficient test
	     * of the full object can be used.
	     */
    	    if(Sgl_iszero(result))
		/* Must have been "x-x" or "x+(-x)". */
		{
		if(Is_rounding_mode(ROUNDMINUS)) Sgl_setone_sign(result);
		*dstptr = result;
		return(NOEXCEPTION);
		}
	    result_exponent--;
	    /* Look to see if normalization is finished. */
	    if(Sgl_isone_hidden(result))
		{
		if(result_exponent==0)
		    {
		    /* Denormalized, exponent should be zero.  Left operand *
 		     * was normalized, so extent (guard, round) was zero    */
		    goto underflow;
		    }
		else
		    {
		    /* No further normalization is needed. */
		    Sgl_set_sign(result,/*using*/sign_save);
	    	    Ext_leftshiftby1(extent);
		    goto round;
		    }
		}

	    /* Check for denormalized, exponent should be zero.  Left    * 
	     * operand was normalized, so extent (guard, round) was zero */
	    if(!(underflowtrap = Is_underflowtrap_enabled()) &&
	       result_exponent==0) goto underflow;

	    /* Shift extension to complete one bit of normalization and
	     * update exponent. */
	    Ext_leftshiftby1(extent);

	    /* Discover first one bit to determine shift amount.  Use a
	     * modified binary search.  We have already shifted the result
	     * one position right and still not found a one so the remainder
	     * of the extension must be zero and simplifies rounding. */
	    /* Scan bytes */
	    while(Sgl_iszero_hiddenhigh7mantissa(result))
		{
		Sgl_leftshiftby8(result);
		if((result_exponent -= 8) <= 0  && !underflowtrap)
		    goto underflow;
		}
	    /* Now narrow it down to the nibble */
	    if(Sgl_iszero_hiddenhigh3mantissa(result))
		{
		/* The lower nibble contains the normalizing one */
		Sgl_leftshiftby4(result);
		if((result_exponent -= 4) <= 0 && !underflowtrap)
		    goto underflow;
		}
	    /* Select case were first bit is set (already normalized)
	     * otherwise select the proper shift. */
	    if((jumpsize = Sgl_hiddenhigh3mantissa(result)) > 7)
		{
		/* Already normalized */
		if(result_exponent <= 0) goto underflow;
		Sgl_set_sign(result,/*using*/sign_save);
		Sgl_set_exponent(result,/*using*/result_exponent);
		*dstptr = result;
		return(NOEXCEPTION);
		}
	    Sgl_sethigh4bits(result,/*using*/sign_save);
	    switch(jumpsize) 
		{
		case 1:
		    {
		    Sgl_leftshiftby3(result);
		    result_exponent -= 3;
		    break;
		    }
		case 2:
		case 3:
		    {
		    Sgl_leftshiftby2(result);
		    result_exponent -= 2;
		    break;
		    }
		case 4:
		case 5:
		case 6:
		case 7:
		    {
		    Sgl_leftshiftby1(result);
		    result_exponent -= 1;
		    break;
		    }
		}
	    if(result_exponent > 0) 
		{
		Sgl_set_exponent(result,/*using*/result_exponent);
		*dstptr = result;
		return(NOEXCEPTION); /* Sign bit is already set */
		}
	    /* Fixup potential underflows */
	  underflow:
	    if(Is_underflowtrap_enabled())
		{
		Sgl_set_sign(result,sign_save);
                Sgl_setwrapped_exponent(result,result_exponent,unfl);
		*dstptr = result;
		/* inexact = FALSE; */
		return(UNDERFLOWEXCEPTION);
		}
	    /* 
	     * Since we cannot get an inexact denormalized result,
	     * we can now return.
	     */
	    Sgl_right_align(result,/*by*/(1-result_exponent),extent);
	    Sgl_clear_signexponent(result);
	    Sgl_set_sign(result,sign_save);
	    *dstptr = result;
	    return(NOEXCEPTION);
	    } /* end if(hidden...)... */
	/* Fall through and round */
	} /* end if(save < 0)... */
    else 
	{
	/* Add magnitudes */
	Sgl_addition(left,right,/*to*/result);
	if(Sgl_isone_hiddenoverflow(result))
	    {
	    /* Prenormalization required. */
	    Sgl_rightshiftby1_withextent(result,extent,extent);
	    Sgl_arithrightshiftby1(result);
	    result_exponent++;
	    } /* end if hiddenoverflow... */
	} /* end else ...add magnitudes... */
    
    /* Round the result.  If the extension is all zeros,then the result is
     * exact.  Otherwise round in the correct direction.  No underflow is
     * possible. If a postnormalization is necessary, then the mantissa is
     * all zeros so no shift is needed. */
  round:
    if(Ext_isnotzero(extent))
	{
	inexact = TRUE;
	switch(Rounding_mode())
	    {
	    case ROUNDNEAREST: /* The default. */
	    if(Ext_isone_sign(extent))
		{
		/* at least 1/2 ulp */
		if(Ext_isnotzero_lower(extent)  ||
		  Sgl_isone_lowmantissa(result))
		    {
		    /* either exactly half way and odd or more than 1/2ulp */
		    Sgl_increment(result);
		    }
		}
	    break;

	    case ROUNDPLUS:
	    if(Sgl_iszero_sign(result))
		{
		/* Round up positive results */
		Sgl_increment(result);
		}
	    break;
	    
	    case ROUNDMINUS:
	    if(Sgl_isone_sign(result))
		{
		/* Round down negative results */
		Sgl_increment(result);
		}
	    
	    case ROUNDZERO:;
	    /* truncate is simple */
	    } /* end switch... */
	if(Sgl_isone_hiddenoverflow(result)) result_exponent++;
	}
    if(result_exponent == SGL_INFINITY_EXPONENT)
        {
        /* Overflow */
        if(Is_overflowtrap_enabled())
	    {
	    Sgl_setwrapped_exponent(result,result_exponent,ovfl);
	    *dstptr = result;
	    if (inexact)
		if (Is_inexacttrap_enabled())
		    return(OVERFLOWEXCEPTION | INEXACTEXCEPTION);
		else Set_inexactflag();
	    return(OVERFLOWEXCEPTION);
	    }
        else
	    {
	    Set_overflowflag();
	    inexact = TRUE;
	    Sgl_setoverflow(result);
	    }
	}
    else Sgl_set_exponent(result,result_exponent);
    *dstptr = result;
    if(inexact) 
	if(Is_inexacttrap_enabled()) return(INEXACTEXCEPTION);
	else Set_inexactflag();
    return(NOEXCEPTION);
    }
Commit	Line	Data
1da177e4 LT	1	/*
	2	* Linux/PA-RISC Project (http://www.parisc-linux.org/)
	3	*
	4	* Floating-point emulation code
	5	* Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
	6	*
	7	* This program is free software; you can redistribute it and/or modify
	8	* it under the terms of the GNU General Public License as published by
	9	* the Free Software Foundation; either version 2, or (at your option)
	10	* any later version.
	11	*
	12	* This program is distributed in the hope that it will be useful,
	13	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	14	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	15	* GNU General Public License for more details.
	16	*
	17	* You should have received a copy of the GNU General Public License
	18	* along with this program; if not, write to the Free Software
	19	* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
	20	*/
	21	/*
	22	* BEGIN_DESC
	23	*
	24	* File:
	25	* @(#) pa/spmath/sfadd.c $Revision: 1.1 $
	26	*
	27	* Purpose:
	28	* Single_add: add two single precision values.
	29	*
	30	* External Interfaces:
	31	* sgl_fadd(leftptr, rightptr, dstptr, status)
	32	*
	33	* Internal Interfaces:
	34	*
	35	* Theory:
	36	* <<please update with a overview of the operation of this file>>
	37	*
	38	* END_DESC
	39	*/
	40
	41
	42	#include "float.h"
	43	#include "sgl_float.h"
	44
	45	/*
	46	* Single_add: add two single precision values.
	47	*/
	48	int
	49	sgl_fadd(
	50	sgl_floating_point *leftptr,
	51	sgl_floating_point *rightptr,
	52	sgl_floating_point *dstptr,
	53	unsigned int *status)
	54	{
	55	register unsigned int left, right, result, extent;
	56	register unsigned int signless_upper_left, signless_upper_right, save;
	57
	58
	59	register int result_exponent, right_exponent, diff_exponent;
	60	register int sign_save, jumpsize;
	61	register boolean inexact = FALSE;
	62	register boolean underflowtrap;
	63
	64	/* Create local copies of the numbers */
65	left = *leftptr;
66	right = *rightptr;
67
68	/* A zero "save" helps discover equal operands (for later), *
69	* and is used in swapping operands (if needed). */
70	Sgl_xortointp1(left,right,/to/save);
71
72	/*
73	* check first operand for NaN's or infinity
74	*/
75	if ((result_exponent = Sgl_exponent(left)) == SGL_INFINITY_EXPONENT)
76	{
77	if (Sgl_iszero_mantissa(left))
78	{
79	if (Sgl_isnotnan(right))
80	{
81	if (Sgl_isinfinity(right) && save!=0)
82	{
83	/*
84	* invalid since operands are opposite signed infinity's
85	*/
86	if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
87	Set_invalidflag();
88	Sgl_makequietnan(result);
89	*dstptr = result;
90	return(NOEXCEPTION);
91	}
92	/*
93	* return infinity
94	*/
95	*dstptr = left;
96	return(NOEXCEPTION);
97	}
98	}
99	else
100	{
101	/*
102	* is NaN; signaling or quiet?
103	*/
104	if (Sgl_isone_signaling(left))
105	{
106	/* trap if INVALIDTRAP enabled */
107	if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
108	/* make NaN quiet */
109	Set_invalidflag();
110	Sgl_set_quiet(left);
111	}
112	/*
113	* is second operand a signaling NaN?
114	*/
115	else if (Sgl_is_signalingnan(right))
116	{
117	/* trap if INVALIDTRAP enabled */
118	if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
119	/* make NaN quiet */
120	Set_invalidflag();
121	Sgl_set_quiet(right);
122	*dstptr = right;
123	return(NOEXCEPTION);
124	}
125	/*
126	* return quiet NaN
127	*/
128	*dstptr = left;
129	return(NOEXCEPTION);
130	}
131	} /* End left NaN or Infinity processing */
132	/*
133	* check second operand for NaN's or infinity
134	*/
135	if (Sgl_isinfinity_exponent(right))
136	{
137	if (Sgl_iszero_mantissa(right))
138	{
139	/* return infinity */
140	*dstptr = right;
141	return(NOEXCEPTION);
142	}
143	/*
144	* is NaN; signaling or quiet?
145	*/
146	if (Sgl_isone_signaling(right))
147	{
148	/* trap if INVALIDTRAP enabled */
149	if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
150	/* make NaN quiet */
151	Set_invalidflag();
152	Sgl_set_quiet(right);
153	}
154	/*
155	* return quiet NaN
156	*/
157	*dstptr = right;
158	return(NOEXCEPTION);
159	} /* End right NaN or Infinity processing */
160
161	/* Invariant: Must be dealing with finite numbers */
162
163	/* Compare operands by removing the sign */
164	Sgl_copytoint_exponentmantissa(left,signless_upper_left);
165	Sgl_copytoint_exponentmantissa(right,signless_upper_right);
166
167	/* sign difference selects add or sub operation. */
168	if(Sgl_ismagnitudeless(signless_upper_left,signless_upper_right))
169	{
170	/* Set the left operand to the larger one by XOR swap *
171	* First finish the first word using "save" */
172	Sgl_xorfromintp1(save,right,/to/right);
173	Sgl_xorfromintp1(save,left,/to/left);
174	result_exponent = Sgl_exponent(left);
175	}
176	/* Invariant: left is not smaller than right. */
177
178	if((right_exponent = Sgl_exponent(right)) == 0)
179	{
180	/* Denormalized operands. First look for zeroes */
181	if(Sgl_iszero_mantissa(right))
182	{
183	/* right is zero */
184	if(Sgl_iszero_exponentmantissa(left))
185	{
186	/* Both operands are zeros */
187	if(Is_rounding_mode(ROUNDMINUS))
188	{
189	Sgl_or_signs(left,/with/right);
190	}
191	else
192	{
193	Sgl_and_signs(left,/with/right);
194	}
195	}
196	else
197	{
198	/* Left is not a zero and must be the result. Trapped
199	* underflows are signaled if left is denormalized. Result
200	* is always exact. */
201	if( (result_exponent == 0) && Is_underflowtrap_enabled() )
202	{
203	/* need to normalize results mantissa */
204	sign_save = Sgl_signextendedsign(left);
205	Sgl_leftshiftby1(left);
206	Sgl_normalize(left,result_exponent);
207	Sgl_set_sign(left,/using/sign_save);
208	Sgl_setwrapped_exponent(left,result_exponent,unfl);
209	*dstptr = left;
210	return(UNDERFLOWEXCEPTION);
211	}
212	}
213	*dstptr = left;
214	return(NOEXCEPTION);
215	}
216
217	/* Neither are zeroes */
218	Sgl_clear_sign(right); /* Exponent is already cleared */
219	if(result_exponent == 0 )
220	{
221	/* Both operands are denormalized. The result must be exact
222	* and is simply calculated. A sum could become normalized and a
223	* difference could cancel to a true zero. */
224	if( (/signed/int) save < 0 )
225	{
226	Sgl_subtract(left,/minus/right,/into/result);
227	if(Sgl_iszero_mantissa(result))
228	{
229	if(Is_rounding_mode(ROUNDMINUS))
230	{
231	Sgl_setone_sign(result);
232	}
233	else
234	{
235	Sgl_setzero_sign(result);
236	}
237	*dstptr = result;
238	return(NOEXCEPTION);
239	}
240	}
241	else
242	{
243	Sgl_addition(left,right,/into/result);
244	if(Sgl_isone_hidden(result))
245	{
246	*dstptr = result;
247	return(NOEXCEPTION);
248	}
249	}
250	if(Is_underflowtrap_enabled())
251	{
252	/* need to normalize result */
253	sign_save = Sgl_signextendedsign(result);
254	Sgl_leftshiftby1(result);
255	Sgl_normalize(result,result_exponent);
256	Sgl_set_sign(result,/using/sign_save);
257	Sgl_setwrapped_exponent(result,result_exponent,unfl);
258	*dstptr = result;
259	return(UNDERFLOWEXCEPTION);
260	}
261	*dstptr = result;
262	return(NOEXCEPTION);
263	}
264	right_exponent = 1; /* Set exponent to reflect different bias
265	* with denomalized numbers. */
266	}
267	else
268	{
269	Sgl_clear_signexponent_set_hidden(right);
270	}
271	Sgl_clear_exponent_set_hidden(left);
272	diff_exponent = result_exponent - right_exponent;
273
274	/*
275	* Special case alignment of operands that would force alignment
276	* beyond the extent of the extension. A further optimization
277	* could special case this but only reduces the path length for this
278	* infrequent case.
279	*/
280	if(diff_exponent > SGL_THRESHOLD)
281	{
282	diff_exponent = SGL_THRESHOLD;
283	}
284
285	/* Align right operand by shifting to right */
286	Sgl_right_align(/operand/right,/shifted by/diff_exponent,
287	/and lower to/extent);
288
289	/* Treat sum and difference of the operands separately. */
290	if( (/signed/int) save < 0 )
291	{
292	/*
293	* Difference of the two operands. Their can be no overflow. A
294	* borrow can occur out of the hidden bit and force a post
295	* normalization phase.
296	*/
297	Sgl_subtract_withextension(left,/minus/right,/with/extent,/into/result);
298	if(Sgl_iszero_hidden(result))
299	{
300	/* Handle normalization */
25985edc	301	/* A straightforward algorithm would now shift the result
1da177e4 LT	302	* and extension left until the hidden bit becomes one. Not
	303	* all of the extension bits need participate in the shift.
	304	* Only the two most significant bits (round and guard) are
	305	* needed. If only a single shift is needed then the guard
	306	* bit becomes a significant low order bit and the extension
	307	* must participate in the rounding. If more than a single
	308	* shift is needed, then all bits to the right of the guard
	309	* bit are zeros, and the guard bit may or may not be zero. */
	310	sign_save = Sgl_signextendedsign(result);
	311	Sgl_leftshiftby1_withextent(result,extent,result);
	312
	313	/* Need to check for a zero result. The sign and exponent
	314	* fields have already been zeroed. The more efficient test
	315	* of the full object can be used.
	316	*/
	317	if(Sgl_iszero(result))
	318	/* Must have been "x-x" or "x+(-x)". */
	319	{
	320	if(Is_rounding_mode(ROUNDMINUS)) Sgl_setone_sign(result);
	321	*dstptr = result;
	322	return(NOEXCEPTION);
	323	}
	324	result_exponent--;
	325	/* Look to see if normalization is finished. */
	326	if(Sgl_isone_hidden(result))
	327	{
	328	if(result_exponent==0)
	329	{
	330	/* Denormalized, exponent should be zero. Left operand *
	331	* was normalized, so extent (guard, round) was zero */
	332	goto underflow;
	333	}
	334	else
	335	{
	336	/* No further normalization is needed. */
	337	Sgl_set_sign(result,/using/sign_save);
	338	Ext_leftshiftby1(extent);
	339	goto round;
	340	}
	341	}
	342
	343	/* Check for denormalized, exponent should be zero. Left *
	344	* operand was normalized, so extent (guard, round) was zero */
	345	if(!(underflowtrap = Is_underflowtrap_enabled()) &&
	346	result_exponent==0) goto underflow;
	347
	348	/* Shift extension to complete one bit of normalization and
	349	* update exponent. */
	350	Ext_leftshiftby1(extent);
	351
	352	/* Discover first one bit to determine shift amount. Use a
	353	* modified binary search. We have already shifted the result
	354	* one position right and still not found a one so the remainder
	355	* of the extension must be zero and simplifies rounding. */
	356	/* Scan bytes */
	357	while(Sgl_iszero_hiddenhigh7mantissa(result))
	358	{
	359	Sgl_leftshiftby8(result);
	360	if((result_exponent -= 8) <= 0 && !underflowtrap)
	361	goto underflow;
	362	}
	363	/* Now narrow it down to the nibble */
	364	if(Sgl_iszero_hiddenhigh3mantissa(result))
	365	{
366	/* The lower nibble contains the normalizing one */
367	Sgl_leftshiftby4(result);
368	if((result_exponent -= 4) <= 0 && !underflowtrap)
369	goto underflow;
370	}
371	/* Select case were first bit is set (already normalized)
372	* otherwise select the proper shift. */
373	if((jumpsize = Sgl_hiddenhigh3mantissa(result)) > 7)
374	{
375	/* Already normalized */
376	if(result_exponent <= 0) goto underflow;
377	Sgl_set_sign(result,/using/sign_save);
378	Sgl_set_exponent(result,/using/result_exponent);
379	*dstptr = result;
380	return(NOEXCEPTION);
381	}
382	Sgl_sethigh4bits(result,/using/sign_save);
383	switch(jumpsize)
384	{
385	case 1:
386	{
387	Sgl_leftshiftby3(result);
388	result_exponent -= 3;
389	break;
390	}
391	case 2:
392	case 3:
393	{
394	Sgl_leftshiftby2(result);
395	result_exponent -= 2;
396	break;
397	}
398	case 4:
399	case 5:
400	case 6:
401	case 7:
402	{
403	Sgl_leftshiftby1(result);
404	result_exponent -= 1;
405	break;
406	}
407	}
408	if(result_exponent > 0)
409	{
410	Sgl_set_exponent(result,/using/result_exponent);
411	*dstptr = result;
412	return(NOEXCEPTION); /* Sign bit is already set */
413	}
414	/* Fixup potential underflows */
415	underflow:
416	if(Is_underflowtrap_enabled())
417	{
418	Sgl_set_sign(result,sign_save);
419	Sgl_setwrapped_exponent(result,result_exponent,unfl);
420	*dstptr = result;
421	/* inexact = FALSE; */
422	return(UNDERFLOWEXCEPTION);
423	}
424	/*
425	* Since we cannot get an inexact denormalized result,
426	* we can now return.
427	*/
428	Sgl_right_align(result,/by/(1-result_exponent),extent);
429	Sgl_clear_signexponent(result);
430	Sgl_set_sign(result,sign_save);
431	*dstptr = result;
432	return(NOEXCEPTION);
433	} /* end if(hidden...)... */
434	/* Fall through and round */
435	} /* end if(save < 0)... */
436	else
437	{
438	/* Add magnitudes */
439	Sgl_addition(left,right,/to/result);
440	if(Sgl_isone_hiddenoverflow(result))
441	{
442	/* Prenormalization required. */
443	Sgl_rightshiftby1_withextent(result,extent,extent);
444	Sgl_arithrightshiftby1(result);
445	result_exponent++;
446	} /* end if hiddenoverflow... */
447	} /* end else ...add magnitudes... */
448
449	/* Round the result. If the extension is all zeros,then the result is
450	* exact. Otherwise round in the correct direction. No underflow is
451	* possible. If a postnormalization is necessary, then the mantissa is
452	* all zeros so no shift is needed. */
453	round:
454	if(Ext_isnotzero(extent))
455	{
456	inexact = TRUE;
457	switch(Rounding_mode())
458	{
459	case ROUNDNEAREST: /* The default. */
460	if(Ext_isone_sign(extent))
461	{
462	/* at least 1/2 ulp */
463	if(Ext_isnotzero_lower(extent) \|\|
464	Sgl_isone_lowmantissa(result))
465	{
466	/* either exactly half way and odd or more than 1/2ulp */
467	Sgl_increment(result);
468	}
469	}
470	break;
471
472	case ROUNDPLUS:
473	if(Sgl_iszero_sign(result))
474	{
475	/* Round up positive results */
476	Sgl_increment(result);
477	}
478	break;
479
480	case ROUNDMINUS:
481	if(Sgl_isone_sign(result))
482	{
483	/* Round down negative results */
484	Sgl_increment(result);
485	}
486
487	case ROUNDZERO:;
488	/* truncate is simple */
489	} /* end switch... */
490	if(Sgl_isone_hiddenoverflow(result)) result_exponent++;
491	}
492	if(result_exponent == SGL_INFINITY_EXPONENT)
493	{
494	/* Overflow */
495	if(Is_overflowtrap_enabled())
496	{
497	Sgl_setwrapped_exponent(result,result_exponent,ovfl);
498	*dstptr = result;
499	if (inexact)
500	if (Is_inexacttrap_enabled())
501	return(OVERFLOWEXCEPTION \| INEXACTEXCEPTION);
502	else Set_inexactflag();
503	return(OVERFLOWEXCEPTION);
504	}
505	else
506	{
507	Set_overflowflag();
508	inexact = TRUE;
509	Sgl_setoverflow(result);
510	}
511	}
512	else Sgl_set_exponent(result,result_exponent);
513	*dstptr = result;
514	if(inexact)
515	if(Is_inexacttrap_enabled()) return(INEXACTEXCEPTION);
516	else Set_inexactflag();
517	return(NOEXCEPTION);
518	}